Combining geothermal energy capture with geologic carbon dioxide sequestration

Abstract

Geothermal energy offers clean, renewable, reliable elec- tric power with no need for grid‐scale energy storage, yet its use has been constrained to the few locations worldwide with naturally high geothermal heat resources and ground- water availability. We present a novel approach with the potential to permit expansion of geothermal energy utiliza- tion: heat extraction from naturally porous, permeable forma- tions with CO2 as the injected subsurface working fluid. Fluid‐mechanical simulations reveal that the significantly higher mobility of CO2, compared to water, at the temperature/ pressure conditions of interest makes CO2 an attractive heat exchange fluid. We show numerically that, compared to con- ventional water‐based and engineered geothermal systems, the proposed approach provides up to factors of 2.9 and 5.0, respectively, higher geothermal heat energy extraction rates. Consequently, more regions worldwide could be economi- cally used for geothermal electricity production. Furthermore, as the injected CO2 is eventually geologically sequestered, such power plants would have negative carbon footprints.